However, speaking to reporters in China, May predicted the vote would damage the economy, and said her government maintained a cautious approach.

"There will be difficult times ahead," May told reporters on her way to a G20 summit in Hangzhou.

"We've seen figures giving some different messages in relation to the economy at the moment. I think the reaction of the economy has been better than some had predicted post- the referendum, but I won't pretend it's going to be all plain sailing."

"What I committed to Theresa is that we will consult closely with her as she and her government move forward with Brexit negotiations to ensure that we don't see adverse effects in the trade and commercial relationship between the United States and the United Kingdom," Obama said.